Doctors in Hanoi separated two four-month-old twin boys on Tuesday by severing a link between a small part of their shared breastbone and liver.

Nguyen Quang Nhat and Nguyen Quang Anh underwent a three-hour surgery at the Central Pediatrics Hospital, nearly 200 kilometers from their home in the mountainous province of Yen Bai.

Dr Pham Duy Hien, deputy head of the surgical department, said the boys’ condition was discovered during an ultrasound conducted during the 20th week of their mother’s pregnancy at the Central Obstetrics and Gynecological Hospital in the capitol.

They were transferred to Hien’s hospital on March 20, five days after a cesarean birth.

Following their delivery, both boys ate and breathed independently.

Hien said the procedure was conducted for free at a time when they were considered strong enough to survive the operation.

Dr Le Thanh Hai, director of the hospital, said the separation of their shared liver was complicated but the “very lucky” the boys were only fused in a small portion of the liver.

Dr Bui Duc Hau, chief surgeon at the hospital, said the operation went smoothly due to the uncomplicated nature of their fusion.

Both boys remain on respirators in infection control rooms.

Doctors said they will remove the post-surgical tubes from the boys in a couple days and they'll be eligible for release in between a week and ten days.

The twins were the sixth pair to have been successfully separated by the hospital since 2003.